C is a typed language, Perl is a dynamic language. I know it is a natural thing to do, but it is dangerous to take a feature of one and try and appy it to another.

Consider it this way. Start with: all Perl subroutines are variadic with no fixed arguments or return type. In C we have variadic functions with a prototype like this:

type myfunc (type arg,...)
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The return type is fixed, but a feature of Perl is that the return type is not fixed - it can be a single value or a collection of values, and that can be a mixture of anything you like. There are no constraints.
In C the type of the first argument is fixed, then all following argument types are determined at runtime. Think what happens in C when you say this:

int i = 42;
printf ("%s\n",i);
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More than likely printf will crash with exception C0000005 on Windows or SIGSEGV on UNIX/Linux. In Perl it won't crash, it will print "42" - it is dynamic.

Yes there are "prototypes" in Perl, but, as moritz said, they are not the same as those in C, they force context not type. You could ask "how do I change a variable's context in C"? It is a daft question, because C does not have context.

Update: some rewording for clarity.